Transformer having a cast winding structure with integral insulating barriers

ABSTRACT

A core and winding assembly insulated by a casing constructed of solid insulating material. Insulating barriers project from the casing to prevent electrical arcing and creepage between winding terminals and the core, and between certain winding terminals. An insulating barrier includes plates orientated in parallel relationship with a gap therebetween to increase the creepage distance. The barriers are formed as an integral part of the casing.

Eley

United States Patent [1 1 [111 3,821,678 [4 June 28, 1974 TRANSFORMERHAVING A CAST WINDING STRUCTURE WITH INTEGRAL INSULATING BARRIERS [75]Inventor: Edgar R. Eley, Athens, Ga. [73] Assignee: WestinghouseElectric Corporation,

Pittsburgh, Pa.

[22] Filed: Oct. 2, 1973 [2]] Appl. No.: 402,683

[52] US. Cl 336/96, 336/192, 336/196 [51 1 Int. Cl. H0lf 27/02 [58]Field of Search 336/96, 196, 198, 205, 336/192 [56] References CitedUNITED STATES PATENTS 3,5l6,040 6/1970 Ripley 336/96 PrimaryExaminer-Thomas J. Kozma Attorney, Agent, or Firm-J. R. Hanway ABSTRACTA core and winding assembly insulated by a casing constructed of solidinsulating material. Insulating barriers project from the casing toprevent electrical arc- 7 ing and creepage between winding terminals andthe core, and between certain winding terminals. An insulating barrierincludes plates orientated in parallel relationship with a gaptherebetween to increase the creepage distance. The barriers are formedas an integral part of the casing.

4 Claims, 5 Drawing Figures PATENTEnJuuza mm FIG. I.

FIG. 3.

IFBG.

TRANSFORMER HAVING A CAST WINDING STRUCTURE WITH INTEGRAL INSULATINGBARRIERS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates, in general, to electrical inductive apparatus and,more specifically, to dry-type transformer insulation structures.

2. Description of the Prior Art Insulating the windings and leads inhigh-voltage, dry-type power transformers requires special considerationof the fact that no liquid dielectric is present as in oil-filledtransformers. In dry-type transformers, it is usually necessary toinsulate the electrical components more completely than in oil-filledtransformers since air'has a lower dielectric constant than mineral oil.This requirement has deterred the use of cast epoxy insulated windingsin dry-type power transformers since the exposed leads from the windingrequire separate insulation structures for proper electricalperformance. Providing such insulation according to conventionalarrangements involves extra labor costs and increases the cost of theapparatus. Therefore, it is desirable, and it is an object of thisinvention, to provide a dry-type power transformer having a cast epoxyinsulation structure which conveniently, economically, and adequatelyinsulates the winding structure and the winding leads.

SUMMARY OF- THE INVENTION There is disclosed herein a new and usefuldry-type power transformer which is sufficiently insulated by an epoxymaterial cast around'a winding of the -trans-' BRIEF DESCRIPTION OF THEDRAWING Further advantages and uses of this invention will become moreapparent when considered in view of the following detailed descriptionand drawing, in which:

FIG. II is a view of a transformer constructed according to thisinvention with the enclosure broken away;

- FIG. 2 is a view of a core and winding structure constructed accordingto this invention;

F IG.-2A is a schematic diagram of the core and winding structure shownin FIG. 2;

F IG'. 3 is a side elevational view of the winding structure shown inFIG. 2; and

FIG. 4 is an end elevational view of the winding structure shown in FIG.3.

DESCRIPI-IONOF THE PREFERRED EMBODIMENTS Throughout the followingdescription, similar reference characters refer to similar elements ormembers in all the figures of the drawing.

Referring now to the drawing, and to FIG. l in partic ular, there isshown a dry-type power transformer ltl constructed according to thisinvention. The trans former enclosure l2 houses the core l4 and thewinding structure 116 of the transformer ill. The mounting frame 18supports the core 114, the winding structure 16, and the terminal board20. Electrical leads 22 connect the terminals on the terminal board 20to terminals extending from the winding structure 116, such as theterminals 24, 26 and 28.

The Winding structure l6 is embedded in a casing constructed from anepoxy resin material. Projections,

or plates, conveniently formed in the epoxy insulating material duringthe casting process, provide the necessary arcing and trackingresistance between various electrical members of the transformer lltl.Various other arrangements of the winding terminals and mountingstructure may be used without departing from the scope of the invention.In this specific embodiment, the epoxy casing encapsulates only thehighvoltage winding of the transformer 10. Although not shown in FIG. I,a non-encapsulated low-voltage winding is located between thehigh-voltage winding and the core 14, and is connected to appropriateterminals which are not illustrated. It is also within the contemplationof this invention that both the high-voltage and the low-voltagewindings could be encapsulated within the same epoxy casing.

FIG. 2 illustrates the core 14 and the winding structure 16 in greaterdetail. The magnetic core 14 includes the wound core sections 32 and 34which each contain an opening through which the winding structure 16extends. An insulating barrier 42 electrically separates the terminals24, 26, 28 and 30 from the magnetic core 14. The barrier 42 must providesufficient dielectric strength and creepage distance to preventelectrical breakdownbetween the terminals and the core 14. This regionis stressed by the maximum potential on the high-voltage winding.

FIG. 2A represents schematically the electrical position of the windingterminals. All of the terminals connected to the high-voltage winding 16must be insulated from the core 14 adequately to protect against themaximum voltage on the winding with respect to ground. The terminal 28must be insulated from the terminals 24, 26 and 30 adequately to protectagainst substantially the maximum voltage across the winding 16. Theinsulation requirements between each of the terminals 36, 38 and 40, andbetween each of the terminals 24, 26 and 30, are not as stringent as theother insulation requirements since the voltage existing between suchterminals is only equal to the voltage developed between a few turns ofthe winding.

Referring again to FIG. 2, the insulating barrier 44 electricallyseparates the terminals 36, 38 and 40 from the magnetic core 14, and theinsulating barrier 46 electrically separates the terminal 28 from theterminals 24, 26 and 3111i. The insulating barrier42 includes the plates48 and 50 which are formed from the epoxy material from which the casing52, which encapsulates the high-voltage winding 16,, is constructed. Theplates 48 and Sll'are orientated substantially parallel to each otherwith a gap 54 located therebetween. The number of plates contained inthe barrier 42 depends largely on the creepage distance necessary toprevent electrical creepage between the core 14 and the terminals 24,26, 28 and 30. The insulating barrier 44 includes the plates 56 and 58which are formed from the same epoxy material and which have a gap 60located therebetween. Similarly, the insulating barrier 46 includes theplates 62 and 64 which are also formed from the same epoxy material asthe casing 52 and which have a gap 66 located therebetween.

FIG. 3 is a side elevational view of the casing 52 which encloses thehigh-voltage winding 16. The inside surfaces 70 and 72 of the casing 52define an opening sufficiently larger than the core 14 to allow forplacement of the low-voltage winding. The distance between the insidesurfaces 74 and 76 shown in the end elevational view of FIG. 4 is alsolarger than the portion of the core 14 to be inserted therein for thesame reason.

The dry-type transformer disclosed herein provides the requiredelectrical insulation characteristics, with a minimum of additionalwork, by forming suitably shaped and positioned insulating barriersduring the encapsulation of thewinding structure with an epoxy material.Since numerous changes may be made in the above-described apparatus, andsince different embodiments of the invention may be made withoutdeparting from the'spirit thereof, it is intended that all of the mattercontained in the foregoing description, or shown in the accompanyingdrawing, shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. A dry-type transformer comprising;

a magnetic core;

a winding assembly inductively coupled to said magnetic core;

a solid electrical insulation structure encapsulating at 4windingassembly and extending through said solid insulation structure;and

barrier means fomiing an integral part of and being of single unitconstruction with said insulation structure, said barrier means having afirst portion projecting between said terminal means and an exposedportion of said magnetic core to provide electrical insulation between.said terminal means and said core and a second portion which extendsbetween the two individual terminals, said second portion including atleast two substantially parallel plates formed of the material fromwhich the insulation structure is constructed, with said platescontaining a gap therebetween which does not contain terminals.

2. The transformer of claim 1 wherein the first portion of the barriermeans includes at least two substantially parallel plates formed of thematerial from which the insulation structure is constructed, with saidplate containing a gap therebetween which does not contain terminals.

3. The transformer of claim 1 wherein the solid electrical insulationstructure and the barrier means are constructed from a materialcontaining epoxy resin.

4. A dry-type transformer comprising:

a wound magnetic core having openings therein;

a tapped winding structure extending through said openings;

an epoxy casing in which said winding structure is encapsulated;

first and second terminals extending from through therebetween'whichdoes not contain terminals.

1. A dry-type transformer comprising; a magnetic core; a windingassembly inductively coupled to said magnetic core; a solid electricalinsulation structure encapsulating at least a portion of said windingassembly, with a substantial portion of said magnetic core being freefrom coverage by said insulation structure; at least two terminalselectrically connected to said winding assembly and extending throughsaid solid insulation structure; and barrier means forming an integralpart of and being of single unit construction with said insulationstructure, said barrier means having a first portion projecting betweensaid terminal means and an exposed portion of said magnetic core toprovide electrical insulation between said terminal means and said coreand a second portion which extends between the two individual terminals,said second portion including at least two substantially parallel platesformed of the material from which the insulation structure isconstructed, with said plates containing a gap therebetween which doesnot contain terminals.
 2. The transformer of claim 1 wherein the firstportion of the barrier means includes at least two substantiallyparallel plates formed of the material from which the insulationstructure is constructed, with said plate containing a gap therebetweenwhich does not contain terminals.
 3. The transformer of claim 1 whereinthe solid electrical insulation structure and the barrier means areconstructed from a material containing epoxy resin.
 4. A dry-typetransformer comprising: a wound magnetic core having openings therein; atapped winding structure extending through said openings; an epoxycasing in which said winding structure is encapsulated; first and secondterminals extending from through said epoxy casing; first and secondepoxy projections of single unit construction with said casing, saidprojections being located between said first and second terminals andsaid core, said first and second epoxy projections having a gaptherebetween; and third and fourth epoxy projections which project fromsaid casing and which are located between said first terminal and saidsecond terminal, said third and fourth epoxy projections having a gaptherebetween which does not contain terminals.